FIGS. 1a-1b represent a modern digital Panoramic/Cephalometric/Cone Beam Computed Tomography (CBCT) combination unit 100 having typically a column 140 that includes an up and down movement Z to adapt a height of the unit 100 to a height of a patient for Panoramic, Cephalometric, and CBCT imaging modes.
An upper shelf 150 of the unit 100 is attached to the column 140 e.g. with a fixed joint. The upper shelf 150 supports a rotating part 120.
The rotating part 120—so-called gantry—has typically a form of a letter C incorporating an X-ray source 124 on one end and an X-ray imaging detector unit 126 on the other end. The rotating part 120 rotates R typically up to 400 degrees around a rotation axis 122.
The X-ray source 124 is common for all the three imaging modes and an X-ray beam limiting device 128 is attached in front of the X-ray source 124.
The detector unit 126 can consist of one or two detectors. The one-detector unit 126 can comprise one Cephalometric detector, which enables also the Panoramic imaging, one Panoramic/CBCT/Cephalometric combination detector, or one shot detector configured to be used in Cephalometric imaging. In two-detector cases, the detector unit 126 can comprise one Cephalometric detector, which enables also the Panoramic imaging, and the CBCT detector. There are several ways to attach the detectors in respect to each other and to change the detector that is located within an X-ray beam.
During imaging, the beam limiting device 128 controls a size and shape of the X-ray beam so that it matches any requirements of a selected imaging mode, selected image size, and related detector size.
The rotation axis 122 fixes the rotation part 120 to the upper shelf 150 and it is typically attached to at least one linear movement so that the rotation axis 122 and, thus, a rotation center of the rotation part 120 in respect to the upper shelf 150 can be adjusted along a Y-movement that is parallel to the upper shelf 150 during the imaging. Furthermore, there can be a second linear X-movement perpendicular to the first one so that the rotation axis 122 can be positioned within a plane defined the linear movements X, Y.
In addition, there can be even a third N-movement that moves a fixing point of the rotation axis 122 in respect to the rotation part 120. Moving the rotation axis 122 along the X-ray beam NA may be used to change a magnification within the Panoramic and CBCT imaging modes. Moving the rotation axis 122 perpendicular to the X-ray beam NP enables a change between offset scanning and symmetrical scanning in the CBCT imaging, thus, affecting the Field Of View (FOV).
A Cephalometric arm 160 is used to attach a. Cephalometric head 162 to the unit 100. It has typically a dedicated X-ray imaging detector 164 at one end and a secondary collimator 166 at the other end. Between these two main parts 164, 166 hang Cephalometric patient positioning support parts 168, 169, which consist of ear rods 168 and a nose (nasion) support 169. The patient's head is supported from an outer part of an ear canal with the ear rods 168 and from a nose using the corresponding support 169.
The Cephalometric X-ray detector 164 is attached to the head 162 with a Cd-movement that moves the detector 164 perpendicularly to the X-ray beam. Alternatively, it is possible to perform the Cephalometric imaging by a one shot technique, when the detector 164 is sufficiently large.
The Cephalometric secondary collimator 166 is also attached to the head 162 with a Cs-movement that is parallel to the Cd-movement and, thus, also perpendicular to the X-ray beam.
The support parts 168, 169 are attached to the head 162 in a manner that enables them to rotate to two main imaging positions: the lateral and posterior anterior (PA) projections. The lateral projection is basically a side view and the PA projection is from a back-to-front view of a skull.
For Panoramic and CBCT imaging, a patient is typically supported by means of a lower shelf 142 and possibly also by means of a temple support 143. The support points are typically a tip of a chin and a forehead or temple of a patient.
The Panoramic imaging unit 100 uses the rotation R and linear X-, Y-, or both X- and Y-movements during the scan resulting in a Panoramic image. Furthermore, depending on the sensor technology used, the image is clocked out using Time Delay Integration (TDI) or full frame read-out mode of the detector. The Panoramic (sharp) layer is defined by the velocities of the movements and, in the case of TDI, the readout rate of the Panoramic detector. When using a full frame detector, the final shape of the layer is calculated on the computer after the scan. Rotation angle is typically about 270 degrees.
In the unit 100 the CBCT imaging is typically implemented by using a rotation movement R and reading out the CBCT detector with a fill frame mode. Thus, projection X-ray images of the Region Of Interest (ROI) are typically produced in a way that the center of the ROI and the rotation movement R coincide. The effective rotation angle (aperture) is ranging typically from approximately 180 to 360 degrees depending on the unit 100.
In the Cephalometric imaging the patient is supported by patient positioning structures 168, 169 located at the Cephalometric head 162 of the unit 100. The X-ray beam is arranged to scan the patient's head with a combination of rotation R and linear Y-movement. The beam is then further collimated by the secondary collimator 166 and finally captured by the Cephalometric detector 164, which both move in synchronism with the beam.